Support 32-bit c++ windows toolchain

[matthauck]

Description of the problem / feature request:

Bazel should support compiling 32-bit c++ build targets on windows.

Feature requests: what underlying problem are you trying to solve with this feature?

I need to compile c++ binaries that run on 32-bit windows.

Bugs: what's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

Tried specifying bazel build ... --cpu x86_32 and bazel build ... --cpu i386 (from bazelbuild/platforms), and both errored out with something like:

ERROR: C:/users/username/_bazel_username/pkyimvir/external/local_config_cc/BUILD:47:1: in cc_toolchain_suite rule @local_config_cc//:toolchain: cc_toolchain_suite '@local_config_cc//:toolchain' does not contain a toolchain for cpu 'x86_32'

What operating system are you running Bazel on?

Windows 10 / Windows 2019

What's the output of bazel info release?

release 2.1.0

Have you found anything relevant by searching the web?

Found claims on stackoverflow that bazel does not support this, and could not find another github issue specifically requesting it.

e.g. https://stackoverflow.com/questions/53291191/compile-a-c-project-wit-bazel-for-x86-32-bit#comment93518681_53318502

[matthauck]

I should add, I think at the very least, this limitation of what is supported built-in should be documented. If it is, I did not come across it. I would much rather have known this at the start of my port to bazel than at the end of it. I did not think to validate that bazel supported building 32-bit binaries. I figured this would just work because there was a --cpu argument. This is pretty painful to realize at the end. 😕

[matthauck]

Ah. looks like #2307 may be the issue of reference.

That was some time ago. Is there still no bandwidth for this?

This should at the very least be documented on the windows support page. (https://docs.bazel.build/versions/master/windows.html)

[matthauck]

Actually. I think that issue is different -- that is about using bazel on 32-bit windows. I want to use bazel on 64-bit windows but produce 32-bit outputs.

[meteorcloudy]

I have a preconfigured version that works for building for x86 32 bit on x64 here: https://github.com/meteorcloudy/my_tests/commits/master/preconfigure_msvc_toolchain